1. Field of the Invention
The invention relates to scrambling and descrambling in communication, and more particularly to a circuit for scrambling a communication packet, a circuit for descrambling a communication packet, a method of scrambling a communication packet, a method of descrambling a communication packet, and a communication device which scrambles and descrambles a communication packet.
2. Description of the Related Art
In a conventional method or apparatus for scrambling and descrambling a communication packet, a cell or frame having a fixed length, such as an asynchronous transfer mode (ATM) cell, is scrambled and descrambled.
The conventional method or apparatus can scramble and descramble only a cell or frame having a fixed length. Specifically, the conventional method or apparatus can scramble and descramble only an area having a fixed length, such as a payload area, in a cell or frame having a fixed length.
Accordingly, the conventional method or apparatus cannot scramble and descramble a cell having a variable length.
Japanese Unexamined Patent Publication No. 11-331803 has suggested a method of ciphering data included in a variable packet. In the suggested method, transport stream packets are grouped into first packets to be ciphered and second packets not to be ciphered. The transport stream packets to be ciphered, that is, the first packets are packets including a head of Packet Elementary Stream (PES) packets arranged in each of payloads of a plurality of transport stream packets. Only data except a header in PES packets included in the payloads of the transport stream packets is ciphered. By ciphering only data included in PES packets at their heads without ciphering the transport stream packets in its entirety, a computer can take PES packets out of the transport stream packets without necessity of deciphering PES packets.
Japanese Unexamined Patent Publication No. 2000-332745 has suggested a transmitter including first means for encoding various contents, second means for storing encoded bit series transmitted from the first means, into a packet, and keeping a part of the packet into secret for producing a packet series, third means for multiplexing a plurality of encoded bit series into a multiplexed bit series in each of packets, based on priority defined in accordance with multiplex delay assigned to each of the encoded bit series, and fourth means for controlling the second and third means. The fourth means updates a scramble key at an interval longer than a maximum multiplex delay time in the multiplexed bit series.
Japanese Unexamined Patent Publication No. 2000-295202 has ebb suggested a receiver system including a transmitter and a receiver. The transmitter includes first means for producing key data used for scrambling a plurality of channel data, and second means for scrambling channel data by virtue of the key data, and the receiver includes third means for descrambling a channel selected among the plurality of channels by virtue of the key data. The transmitter scrambles a plurality of channels by virtue of common key data, and the receiver includes fourth means for storing the common key data. Even if any channel is selected, the selected channel is descrambled by virtue of the common key data stored in the fourth means.
Japanese Unexamined Patent Publication No, 9-321750 has suggested a method of making scrambling communication between a transmitter and a receiver through a network, including the steps of dividing original data into a plurality of packet-sized data, storing the packet-sized data into a packet, assigning a false packet identifier indicative of an order of scrambled packets, to the packet, and transmitting the packet into a network in an order in which packets are scrambled in accordance with the false packet identifier. These steps are carried out at the side of the transmitter. The method further includes the steps of reproducing data indicative of a true data order, based on the false packet identifier, and reconstructing the original data, based on the true data order. These steps are carried out at the side of the receiver.
Japanese Unexamined Patent Publication No. 10-241288 has suggested an apparatus for receiving and reproducing multiplexed data. Multiplexed data has a packet structure having an inherent and fixed length, ID data for defining the packet structure, and an inherent data rate. The suggested apparatus includes first means for receiving the multiplexed data, second means for extracting desired service data, based on the ID data included in the received multiplexed data, third means for storing the extracted service data in either the apparatus or a first data-reproducer, fourth means for adding a first dummy packet having a particular ID for identifying a packet, to the extracted service data, ill accordance with both the inherent data rate of the extracted service data and a data-recording rate of the first data-reproducer, when the extracted service data is stored into the first data-reproducer, fifth means for reading the extracted service data out of the first data-reproducer, sixth means for deleting the first dummy packet from the extracted service data read out of the first data-reproducer, and seventh means for reproducing the service data from which the first dummy packet was deleted.